Eruvin 3a

עירובין ג׳ ע״א

Learn Eruvin 3a step by step: Aramaic beside English, every question, answer and proof colour-coded.

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Topic

The twenty-אמה height limit for a מבוי's קורה and for סוכה: the אמלתרא (cornice) exception, the idea of noticeability, and a beam or סכך that is partly above twenty.

Overview

Earlier on the daf, רב learned the twenty-אמה limit for the קורה of a מבוי from the twenty-אמה doorway of the היכל. The גמרא challenges him: the היכל had אמלתראות (decorative cornices) and was still only twenty high, yet רב is quoted as saying a קורה with an אמלתרא works even above twenty. רב יוסף says the cornice rule is really a ברייתא, but אביי shows that a reliable teacher taught it. רב is then defended in two ways. Either the two ברייתות reflect a מחלוקת תנאים, or, as רב נחמן בר יצחק says, a קורה works because it is noticeable, so a cornice still works high up and the היכל is only a memory aid. The גמרא explains why רבי יהודה and the רבנן argue about height for both סוכה and מבוי, and then gives two definitions of אמלתרא: nest-shaped carvings or valuable cedar poles. Next it asks about a beam or סכך that is partly below and partly above twenty אמות. There are two opposite versions of רבה's ruling, each explained by רבא מפרזקיא and רבינא. Finally the גמרא asks for the practical הלכה: רבה בר רב עולא says both cases are פסול, and רבא says both are כשר, a statement that continues on the next amud.

Opening lines

The steps (37)

1. ChallengeA cornice should not help if רב learns from the היכל
2. ProofProof from the משנה of five oak cornices
3. RejectionPerhaps the cornices were on the Entrance Hall
4. RejectionThe Sanctuary may have been built like the Entrance Hall
5. Challengeרב himself says a cornice allows a beam above twenty
6. RejectionThe cornice rule is only a ברייתא of unknown authority
7. ChallengeA reliable teacher taught it, so the challenge returns
8. Resolutionרב answers: it is a dispute between תנאים
9. ResolutionThe ברייתות agree: the beam is a marker and the היכל is a memory aid
10. ChallengeSetting up a problem for רב נחמן בר יצחק using רבה's teaching on סוכה
11. ChallengeWhy would the תנאים argue about the same point twice?
12. ResolutionBoth disputes are needed because סוכה and מבוי are used differently
13. QuestionWhat exactly is an אמלתרא?
14. Responseרב חמא בריה דרבה בר אבוה: carvings shaped like birds' nests
15. ResponseIn ארץ ישראל they say it means cedar poles
16. StatementThe practical difference between the two definitions
17. QuestionWhy would cedar poles make the beam noticeable?
18. ResponseFirst answer: the poles are long
19. ChallengeA סוכה is also long, yet it is still invalid
20. ResolutionBetter answer: cedar is valuable, so people talk about it
21. QuestionWhat if part is below twenty and part is above?
22. Responseרבה: valid in a מבוי, invalid in a סוכה
23. ChallengeWhy not 'thin out' the סכך just like the beam?
24. ResolutionThinning the סכך would leave more sun than shade
25. RejectionThe beam would also be too weak, so both must be accepted
26. ResolutionOne person forgets, but many people remind each other
27. ResolutionTorah law is treated strictly, rabbinic law leniently
28. StatementA reversed version of רבה's ruling
29. ChallengeWhy not apply the thinning logic to the beam too?
30. ResolutionA thinned beam would blow away in the wind
31. RejectionIf thinned סכך still gives shade, a thinned beam is still sturdy
32. ResolutionOne owner remembers, many owners forget
33. ProofThe partners' pot proverb
34. ResolutionA rabbinic law needs extra strengthening
35. QuestionWhat is the final הלכה?
36. ResponseBoth are invalid
37. ResponseBoth are valid